1. Field of the Invention
The present invention relates to a chain wheel assembly for a bicycle having at least one large chain wheel, at least one small chain wheel, and a crank arm for driving the chain wheels, and to the crank arm for use with this chain wheel assembly.
2. Description of the Related Art
In a conventional chain wheel assembly, as shown in FIG. 13, a crank arm 1 includes a wheel mount 10 having a connecting portion 10a for connecting a large chain wheel 5. Thus, the large chain wheel 5 is connected directly to the crank arm 1.
With the above conventional structure, where the large chain wheel has an increased inside diameter to be lightweight, the wheel mount of the crank arm must extend to a large extent from a boss of the crank arm connected to a crank axle. Consequently, when such crank arms are manufactured by casting, unacceptable products often occur for lack of molten metal reaching corners of dies to form the wheel mount. In the case of forging, a large quantity of material is needed to obtain large crank arms. This results in an increased material cost, and a troublesome manufacturing process with an additional operation to cut the forged crank arms to shape.